The relationship between work during pregnancy and the weight of an infant at birth is poorly understood and has not been explored in detail in any U.S. populations. If working during pregnancy places women at increased risk of delivering either preterm or term low birthweight babies, that information is critical for health care providers to advise appropriately and for policy makers to develop adequate benefit packages and workplace regulations. The proposed analysis is based on a subsample of 3,088 single live births to white, married women, 18-35 years, who worked during the twelve months before delivery and responded to the occupation questions in the 1980 National Natality Survey (NNS). Three major hypotheses regarding the independent relationships of physical work stress and intensity of work during pregnancy to term and preterm low birthweight as well as the combined effect of the independent variables to the same outcomes will be tested. In the analyses, maternal education, parity, pregnancy complications, smoking, weight gain and adequacy of prenatal care utilization will be controlled. To construct measures of physical stress at work, NNS data will be matched with descriptive data on occupations from the Dictionary of Occupational Titles (DOT). Confirmatory factor analysis will be used to create a physical work stress factor from DOT "physical demands" and "working conditions" variables. To test the hypotheses, multiple regression, logistic regressing and covariance structure modelling will be used.